Problems swapping C drives when also using a single D drive.

I'm going on the concept that you don't need to run two versions of Windows. There was a time, way back even before XP that you would configure two hardware profiles, but those days are long, long gone. If you build one install that's optimized, you can use it for all of your needs. K.I.S.S. is the motto.

having major issues now. Can't access the D drive at all. Keep getting the following popup which I haven't seen before. Any Ideas?
Even if I can drag the data off and reformat.